The invention relates to hydrotreating and hydrocracking vacuum gas oil, Diesel, kerosene and naphtha fractions obtained from a vacuum residue hydrocracking (VRHCK,) using a high temperature and high pressure stripping and washing stage for connecting two high pressure reaction zones. More particularly, the invention relates to a hydrotreating and/or hydrocracking process using a high pressure, high temperature stripping and washing process which is well suited as an intermediate step integrated into a high temperature and high pressure loop of a vacuum residue hydrocracking (VRHCK) process wherein the VRHCK process and stripping-washing step produce kerosene, naphtha, Diesel and vacuum gas oil feeds to a hydrotreating-hydrocracking reactor for reducing sulfur content and improving naphtha, kerosene and Diesel yields and quality; in particular to produce a high smoke point kerosene, high cetane number and low sulfur Diesel and a low sulfur naphtha fractions.
Many refineries hydrotreat virgin and cracked feedstocks in order to obtain upgraded gasoline and Diesel products. These refineries utilize high-pressure units. High pressure hydrodesulfurization (HDS) units can be utilized with cracked vacuum gas oil (VGO), and when operated between 700-1200 psig, can achieve HDS conversion rates of greater than 99% so as provide a product having a sulfur content between 0.002 and 0.12% wt. This product can then be fed to a fluid catalytic cracking (FCC) process to produce gasoline and Diesel fuel with sulfur content less than 150 ppm and 600 ppm respectively. Unfortunately, the Diesel fraction produced in an FCC process from such a VGO feed typically has a cetane number of only about 20-30, which is considered xe2x80x9cout of specxe2x80x9d and prevents this product from being incorporated into the Diesel pools. In order to be used, this Diesel fraction must be treated with additional hydrotreating steps. In addition, numerous other Diesel streams are readily available in the refineries such as straight run kerosene and Diesel, thermal cracked Diesel and the like, all of which have high sulfur content and typically medium cetane number that will require an additional deep hydrotreatment.
Conventional low-medium pressure Diesel hydrotreatment can satisfactorily reduce the sulfur content, but provides only small improvements in cetane number, in the range of 2-4 point increments.
Some refineries have installed residue hydrocracking units to convert the heaviest part of the oil into distillates. All of these technologies produce a medium quality product that requires an additional high pressure hydrotreating stage in a separate unit to fulfill the pool specifications. They also produce a large amount of VGO that needs to be converted in standard fluid catalytic cracking or hydrocracking units.
Typical catalysts for use in hydrotreating-hydrocracking processes to increase cetane number and smoke point and to reduce sulfur to very low level are extremely sensitive to even small amounts of sulfur and ammonia, and therefore cannot readily be incorporated into hydrotreating-hydrocracking reactors.
Alternatives for processing all the naphtha, kerosene, Diesel and VGO to solve the yield and quality problem identified above include integrating a high pressure hydrotreating and hydrocracking reactor into an existing or new vacuum residue hydrocracking technology for sequentially hydroprocessing-hydrocracking the available xe2x80x9cout of specxe2x80x9d products. That effort attempts to address the yield, sulfur, smoke point and cetane number objectives by using two or more stages of hydroprocessing. Unfortunately, conventional vacuum residue hydrocracking units require a conventional separation process where the products are cooled and depressurized to be able to separate and then treat those products in a stand alone hydrotreating or hydrocracking or FCC unit. These conventional separation processes are carried out at low temperature, low pressure, or both, resulting in the need for additional compression systems, one for each stage, which can double equipment and operation costs. Even then, a complete and potentially very expensive hydrotreating-hydrocracking-FCC unit is required.
It is clear that the need remains for a method for treating feedstocks such as vacuum gas oil, kerosene, Diesel and naphtha, xe2x80x9cout of specxe2x80x9d product from primary conversion (VRHCK), and others such as Diesel and naphtha fractions available in the refinery, so as to advantageously improve yields and reduce sulfur content while improving smoke point and cetane number. Further, the need remains for a process whereby separation of components is achieved at high temperature and pressure so as to avoid the need for additional compression equipment and the like. Still further, the need remains for a process to hydrofinish the product without the need to buy additional complete hydrotreating-hydrocracking units.
It is therefore the primary object of the present invention to provide a process whereby VGO, kerosene, Diesel, and naphtha xe2x80x9cout of specxe2x80x9d feedstocks can advantageously and economically be converted into valuable end products.
It is another object of the invention to provide a process which can advantageously find use in revamping existing facilities or building new ones.
It is a further object of the invention to provide a process for high pressure and high temperature separation to produce an intermediate feedstock that can be blended with an external VGO, Diesel and naphtha xe2x80x9cout of specxe2x80x9d component to be sequentially hydrotreated or hydrocracked in subsequent hydrotreating-hydrocracking reaction stages.
It is still another object of the present invention to utilize the existing high pressure and temperature loop in a vacuum residue hydrocracking unit or process to provide an integrated process which sequentially integrates a hot separation-stripping washing system into a vacuum residue hydrocracking process with a further hydrotreating-hydrocracking stage or stages so as to advantageously and efficiently provide for excellent conversion rates in converting the VGO, kerosene, Diesel and naphtha feeds to desirable end product, while nevertheless minimizing expense due to equipment costs and efficiently utilizing high pressure and temperature conditions.
Other objects and advantages will appear herein below.
In accordance with the present invention, the foregoing objects and advantages have been readily attained.
According to the invention, a process is provided for sequentially hydrotreating vacuum gas oil, kerosene, Diesel and naphtha, which process comprises the steps of providing a reaction feed containing residue, vacuum gas oil, kerosene, naphtha, Diesel, hydrogen sulfide, ammonia, and C1-C4 gas phase compounds; providing a stripping gas; providing a washing feed; and feeding said reaction feed, said stripping gas and said washing feed to a stripping and washing zone so as to obtain a gas phase containing said hydrogen sulfide, said ammonia, said C1-C4 gas phase compounds, said naphtha, said kerosene, said Diesel and said vacuum gas oil and a liquid phase, wherein said reaction feed is provided at a reaction feed pressure of between about 700 psig and about 3500 psig, and wherein said stripping and washing zone is operated at a pressure within about 80 psig of said reaction feed pressure. The hydrotreating-hydrocracking reactors, as well as the stripping/washing separator, are advantageously operated at substantially the same pressure, and preferably substantially the same temperature, thereby avoiding the need for additional compressor equipment between stages and limiting the need for additional heating between stages as well, while utilizing the already established temperature and pressure from the VRHCK loop to carry out further improvement as desired.
The inventive separation-reaction process can advantageously be used to integrate hydrotreatment-hydrocracking processes which occur at high temperatures and pressures so as to sequentially treat vacuum gas oil, kerosene, Diesel, naphtha and other feeds to obtain high conversion to desirable products at reduced cost.